Replacement of the aortic valve or the full aortic root can be performed using a variety of stentless valve devices. The three main options are a porcine aortic root-valve conduit (Medtronic Freestyle, Medtronic Inc., Minneapolis, MN), and the “human” valve options of the aortic homograft and the pulmonary autograft (Ross Procedure). Having reviewed the subject almost 30 years ago,¹ it is interesting to note how some things have changed but much has remained the same. Table 29-1 summarizes advantages and disadvantages of current replacement options.

The first choice for aortic valve replacement (AVR) was the homograft aortic valve. Gordon Murray created an animal model to implant an aortic homograft valve in the descending aorta² and was the first to apply the concept in the human demonstrating function for up to 4 years.³

Duran and Gunning at Oxford described a method for orthotopic (subcoronary) implantation of an aortic homograft valve in 1962⁴ and in 1962 both Donald Ross in London,⁵ and Sir Brian Barratt-Boyes in Auckland,⁶ did this successfully in humans.

Initially, homograft aortic valves were implanted shortly after collection.⁷ This impractical method was rapidly supplanted by techniques to sterilize and preserve the valve for later use. Early methods employed beta-propiolactone^6,8 or 0.02% chlorhexidine,⁹ followed by ethylene oxide or radiation exposure.¹⁰ Some were preserved by freeze-drying.^6,10 Recognizing that the incidence of valve rupture was high in chemically treated valves, Barratt-Boyes introduced antibiotic sterilization of homografts in 1968.¹¹ Cryopreservation of allografts was introduced in 1975 by O’Brien and continues to be the predominant method.^12,13 Experimental use of autologous valve transplantation began in 1961 when Lower and colleagues at Stanford transposed the autologous pulmonic valve to the mitral position in dogs¹⁴ and shortly thereafter to the aortic position.¹³ Donald Ross applied this to humans, reporting in 1967 clinical experience replacing either the aortic or the mitral valve with a pulmonary autograft.¹⁴ Nearly 20 years later the autograft was finally done in America by Elkins and Stelzer.¹⁵ The operation came to be known as the Ross procedure. After an initial surge of interest in the 1990s (over 240 surgeons worldwide reported their experience to the Ross Procedure International Registry¹⁶), its use diminished in the next decade.

The porcine aortic root (Medtronic Freestyle aortic root bioprosthesis (Medtronic Inc., Minneapolis, MN)) is readily available preserved in glutaraldehyde (Fig. 29-1). Its “off the shelf” availability in a wide range of sizes make it a more flexible option compared to the homograft which is limited in both number and size by the tissue donor pool and what is available in the tissue bank. The Freestyle porcine root employed third-generation tissue technology with zero-pressure fixation and treatment with alpha amino oleic acid (AOA) which aims to decrease both leaflet and aortic wall calcification. This device first began with clinical investigation in 1992. It employed zero-pressure glutaraldehyde fixation and AOA treatment to enhance durability as a third-generation tissue valve. It was approved for clinical use in 1998. The conduit is a complete porcine aortic root with a 3-mm rim of polyester fabric along the proximal end providing additional strength for suturing.

Cellular and Immunologic Aspects of Homografts

The normal living valve contains multiple viable cell types including endothelial cells, fibroblasts, and smooth muscle cells incorporated in a complex extracellular matrix. The cells and matrix elements are in a constant state of remodeling under the influence of regulatory systems that optimize the structure and function of the valve mechanism. It is understandable, therefore, that efforts to preserve homograft structure and function were translated into efforts to maintain homograft cellular viability. Radiation and chemical treatment led to very early failure and were quickly abandoned.^6,8,10,11,17 Antibiotic sterilization of homografts and storage at 4°C does not maintain cellular viability beyond a few days.^18,19 Cryopreservation became the gold standard when donor fibroblast viability was shown long after implantation.¹² Although antigenicity of the fibroblast is low and other cell types do not survive the freezing process, panel reactive antibody and donor-specific HLA I and II antibody testing is positive in 60 to 80% of homograft recipients.^20-22 The potential advantages of viability may be defeated by the detrimental effects of this immune system response. Animal studies have confirmed an immune mechanism by demonstrating that deterioration in homograft valve function is prevented by immunosuppression²³ and does not occur in T-cell-deficient rats.²⁴ Clinical use of immunosuppression, however, could not be justified for homograft patients.

Tissue engineering concepts led to decellularization which lyses cells and “rinses” out antigenic proteins leaving an inert matrix and intact structural framework. Preserved mechanical properties and structural integrity were demonstrated in a sheep model of such a scaffold. In addition, the empty matrix seemed to attract circulating recipient stem cells which repopulated the framework and differentiated into appropriate cell lines capable of maintaining the matrix.²⁵ Initial use of the decellularized aortic homograft in humans demonstrated that structural integrity could be maintained with low, stable gradients and minimal regurgitation similar to standard cryopreserved homografts.²⁶ The same concept has been applied to the pulmonary homograft used in the Ross operation.^27,28 The decellularized aortic homograft has been largely abandoned because of early failure rates but the decellularized pulmonary homograft has been at least as good or better than the standard pulmonary homograft when used on the right side of the heart.²⁹ Long-term studies are needed to determine if native cell in growth occurs reliably. A decellularized xenograft valved conduit has also been used successfully for the right ventricular outflow tract (RVOT) reconstruction with the Ross but results were poor.³⁰

In summary, despite intensive investigation over decades, the relative contribution of the immune response, preservation techniques, and warm ischemia time to ultimate valve degeneration is not clear. More importantly, after consideration of the structural benefits and the immune-reaction risks, the net advantage of maintaining cellular (particularly fibroblast) viability in the homograft is not well defined.³¹

Indications for the Porcine Xenograft (Freestyle) and Aortic Homograft

AVR with a stentless valved conduit such as the porcine root or aortic homograft has a number of advantages including excellent hemodynamic profile with low transvalvular gradients and possibly enhanced regression of left ventricular mass,³² low risk of thromboembolism without the need for systemic anticoagulation, and low risk of prosthetic valve infection. However, these conduits are subject to structural deterioration that is inversely proportional to recipient age. Older homograft donor age may also increase rates of degeneration. Furthermore, the availability of homografts is still limited especially in the larger sizes. The strongest indication for a homograft is for treatment of active aortic valve endocarditis particularly in patients with root abscess, fistula formation, or prosthetic valve infection.³³ This is the only Class I indication for a homograft in the most recent guidelines.³⁴

The porcine root is also an option in aortic valve endocarditis with root destruction requiring a root replacement with the advantage that it possesses minimal prosthetic material compared with a polyester valved-conduit graft. The pliable handling characteristics and ease of coronary reimplantation make both the homograft and porcine root a great option in root infections. The homograft is further well suited to this challenging task as it comes with the added benefits of having the attached donor mitral anterior leaflet, and the ability to reconstruct the debrided root with all biological material to minimize risk of persistent infection. The homograft’s very low early hazard rate for endocarditis sets it apart from other valve alternatives.³⁵

The stentless porcine root and aortic homograft are also a reasonable option in the older patient (>60 years of age) with a small aortic root. The hemodynamic advantages of the homograft translate into better relief of outflow obstruction and improved exercise tolerance. The root replacement option also eliminates the risk of coronary obstruction from an oversized aortic prosthesis. Given its resistance to thromboembolic complications the aortic homograft can also be considered for younger patients requiring composite aortic valve or root replacement who cannot be anticoagulated. However, recent data from a prospective randomized trial would argue that most of the advantages of the homograft can be duplicated by the stentless porcine root replacement which has a significantly lower reported rate of calcification and valve dysfunction.³⁶

Preoperative Evaluation

Preoperative transthoracic echocardiography (TTE) is an invaluable diagnostic tool for evaluation of the AV and associated anatomic structures. Echo measurement of the left ventricular outflow tract can accurately predict aortic annulus diameter and thus the size of the porcine root/homograft required.^37-39

Computed tomographic angiography (CTA) or cardiac magnetic resonance (CMR) imaging can also be very useful in the evaluation of potential homograft patients particularly those with aortic root abscess (see Fig. 29-2). Coronary angiography should be employed with the standard indications but may be hazardous in patients with mobile vegetations on the aortic leaflets. Standard chest computed tomography with and without contrast should be considered in any reoperative setting to assess location of bypass grafts, proximity of vital structures to the sternum, and extent of ascending aortic or arch calcification or aneurysm. Heavy calcification around the coronary ostia may preclude safe reimplantation of coronary “buttons” or even a distal subcoronary suture line.

Transesophageal echocardiography (TEE) is often necessary to establish the presence of a root abscess, but its major role is for intraoperative confirmation of the anatomy and assessment of both valve and ventricular function.

General Preparation

Routine cardiac surgical monitoring including TEE is considered standard of care. An antifibrinolytic agent such as epsilon-aminocaproic acid is helpful. A standard midline sternotomy incision provides full exposure of the heart, ease in cannulation, and access for optimal myocardial protection. Routine distal aortic cannulation and a dual stage venous cannula can usually be employed.

Unless circulatory arrest is needed, minimal systemic cooling (32^°C) is adequate if the heart is maintained at 10 to 15^°C using a standard insulating pad and directly monitoring the myocardial septal temperature. A combination of antegrade and retrograde cold blood cardioplegia can be used with the bulk of the protection coming from the retrograde. The open aortic root reveals coronary return from both ostia to confirm effective retrograde.

A transverse aortotomy high (1.5–2 cm) above the commissures is usually best. The diseased aortic valve is excised and the annulus is measured with cylindrical sizers. The sinotubular junction should also be evaluated for the subcoronary technique. If using the porcine root, its size can then be confirmed and the prosthesis opened and rinsed.

If using the homograft, sufficient time (20 minutes) is required to thaw the prosthesis and so a decision to use the homograft with a specific size is required prior to exposing the root and sizing it directly. Hence the measurement of the aortic annulus on TEE is essential after induction of anesthesia allowing the time to ensure that the appropriate sized conduit is available onsite.

The homograft is trimmed appropriately. In general, 3 to 4 mm of tissue proximal to the nadir of each cusp is advised for security in suture placement leaving even more for full root replacements.

Techniques of Porcine Root/Homograft Placement

SUBCORONARY IMPLANT TECHNIQUE

The subcoronary method involves two suture lines within the native root. The prosthesis is usually oriented anatomically to properly align the commissures and the coronaries. The proximal end of the prosthesis is sewn to the native annulus in a circular plane at the level of the nadir of each sinus curving upward slightly in the membranous septum to avoid injury to the conduction system. This anastomosis can be done with either interrupted or continuous sutures (see Figs. 29-3 and 29-4).

The top of each commissure is tacked to the aortic wall. The right and left sinus walls are then scalloped out to a point 3 to 5 mm from the leaflets. The noncoronary sinus can also be removed but is usually left intact. A 4-0 or 5-0 polypropylene suture is started at the lowest point under each coronary ostium and a continuous suture line constructed from there up to the top of the commissure on either side. On the top of the noncoronary sinus, excess prosthetic tissue is trimmed down and tacked to the top of the aortotomy. The aortotomy is then closed with continuous 4-0 polypropylene suture incorporating the top of the prosthesis noncoronary sinus with the native aortic wall. The ascending aorta is vented as the aortic clamp is removed. TEE can quickly assess any regurgitation at this point. Distension of the ventricle should be avoided by prompt defibrillation (if necessary) and pacing if required.

Because even slight malalignment of the commissures can result in regurgitation, the subcoronary implant technique is considered more demanding than the other techniques and may have poorer long-term results.^40-44 The subcoronary technique is good for patients with small, symmetric aortic roots and sinotubular junctions, while it is a poor choice for those with dilated, asymmetric, or severely diseased roots.

Porcine Root/Homograft Cylinder: Inclusion Root Technique

The cylinder modification of the subcoronary technique was developed in an attempt to preserve the native geometry of the prosthesis inside the recipient aortic root. The proximal suture line is identical to the subcoronary method but the sinuses are not scalloped out. Instead, a buttonhole is made in the right and left sinuses in such a way as to allow the porcine root/homograft wall to be sewn to the native sinus wall around the coronary ostia. After the coronaries are secure, the distal end of the prosthesis is attached at the commissures and then incorporated circumferentially into the aortotomy closure.

Sievers and colleagues⁴⁵ and Skillington⁴⁶ have carefully described technical aspects of these operations that have proven very effective in their hands and should be reviewed by surgeons interested in using this method.

Porcine Root/Homograft Root Replacement

The root replacement technique can be used in any root and is particularly useful in small roots or in roots destroyed by endocarditis. The root replacement allows size flexibility that allows thawing an appropriate homograft without wasting clamp time. Very large roots may require commissural plication as described by Northrup.⁴⁷

The aorta is opened transversely well above the commissures of the valve. The diseased valve is excised and annulus debrided. The aorta is transected and the coronary ostial buttons are mobilized in standard fashion. If antegrade cardioplegia is used after this point it must be done very carefully to avoid injury to the mobilized ostia.

The homograft root is usually oriented anatomically while the porcine root is commonly oriented with the left coronary os matching that of the patient’s right coronary—making matching the two roots easiest. (Porcine coronaries are closer together than human.) The proximal suture line can be constructed with either continuous or interrupted technique. Interrupted is best in difficult reoperations especially for prosthetic valve endocarditis (PVE) because it allows for very accurate, deep placement of individual stitches while distributing tension across multiple sutures. A strip of autologous (or bovine) pericardium is used to reinforce this crucial anastomosis. Polypropylene sutures of 3-0 or 4-0 are used and organization scrupulously maintained on suture guides. The homograft parachutes down as the sutures are carefully tightened (Fig. 29-5).

The Freestyle root is most often sutured with a continuous suture technique with 4-0 polypropylene begun at the right-left commissure and sewing towards oneself through the left sinus, then the noncoronary and finally the right sinus to end at the noncoronary-right commissure. The fibrous trigones and commissures of the native and homograft/Freestyle roots serve as anatomical landmarks and should match up as one proceeds around. It is recommended that the valve be sewn with the sutures kept loose during the left and noncoronary sinus suturing and the conduit parachuted down progressively. Keeping the suture line loose is essential to completing the right sinus suture line. Once all the sutures have been placed, the initially loose suture line is tightened carefully with nerve hooks and tied securely into position. Gentle tissue handling with bites 1.5 to 2 mm apart incorporating a strip of pericardium or Teflon felt is helpful in securing hemostasis at this crucial level that is virtually invisible at the end.

The coronary buttons are attached with continuous 5-0 or 6-0 polypropylene. The coronary stumps of the homograft often times are well aligned to mark locations for the new coronary ostia. For the porcine root usually the left ostium of the porcine root will line up with the left button and then one has to determine if the right ostium lines up appropriately or whether it needs to be suture ligated and another hole made for the right button. Rotating the device 120° clockwise puts the porcine left in the patient’s right if that looks better. Once the buttons are completed attention can be turned to the distal anastomosis. The distal end of the conduit and the native aorta are trimmed and sewn together with continuous 4-0 polypropylene usually incorporating another strip of pericardium or felt for support. The native aorta is vented anteriorly and systemic flow rate lowered as the cross clamp is removed.

Care is taken to avoid systemic hypertension or vigorous traction on the reconstructed root to avoid bleeding. Topical hemostatic agents and biological glues may be used, but they should not be routinely necessary. Blood and blood products are not routinely required unless the patient is coagulopathic or small in size with a low total blood volume.

Post Replacement Assessment

Ventricular function, regional wall motion abnormalities, and valve function may all be accurately determined with TEE. With appropriate loading conditions, moderate-to-severe aortic regurgitation (AR) warrants inspection and revision of the valve conduit. Mild AR is usually tolerated well and does not warrant reexploration.

Postoperative Management

Even mild hypertension should be avoided to prevent disruption of crucial aortic suture lines. Coagulopathic bleeding is best addressed with products targeted to specific abnormalities defined by laboratory studies.

Adequate volume replacement is required to keep the stiff ventricle of aortic stenosis (AS) filled and alpha adrenergic support is often required for the patient who is vasodilated. Atrial rhythm disturbances should be treated aggressively. Elderly patients, particularly females, with AS and diastolic dysfunction are at increased risk of morbidity and even mortality from postoperative atrial fibrillation. The increased volume loading needed to overcome the loss of atrial transport often leads to pulmonary congestion sometimes requiring reintubation and prolonged support. Forward cardiac output is impaired and renal function may deteriorate in tenuous patients. Cardioversion should be considered early in these patients and loading with intravenous amiodarone is usually indicated. Preoperative loading with amiodarone may minimize the incidence and consequences of this arrhythmia.⁴⁸

Temporary pacing, preferably atrial as well as ventricular, should be enabled. Permanent pacing is indicated if epicardial wires become unreliable, heart block was present preoperatively, or the underlying rhythm fails to return within a week after surgery.

Stroke risk can be minimized by careful intraoperative epi-aortic ultrasound to guide or avoid cannulation and clamping of atheromatous aortic disease. TEE-guided evacuation of air is essential and flooding the field with carbon dioxide may be helpful.

Myocardial dysfunction is best prevented by careful temperature-monitored myocardial protection but long operations may still require temporary inotropic support. Caution must be used in the hyperdynamic ventricle with diastolic dysfunction. The combination of a hyperdynamic left ventricle and a dysfunctional right heart is very challenging. These patients may benefit from atrial pacing (if pacing is required), phosphodiesterase inhibitors, adequate volume replacement, and alpha agonists.

Renal insufficiency is a risk minimized by maintenance of adequate flows and pressure during bypass and generous volume administration in the early postoperative period. A thirsty patient with dry mucous membranes is a good clue that intravascular volume is still depleted. Later, diuretics are needed to encourage mobilization and excretion of this extra fluid. Hypotension should be avoided but vasopressors can have direct negative effects on renal blood flow.

Low-dose aspirin is often recommended for homograft patients, but is not necessary and formal anticoagulation with warfarin is not required at all unless dictated by other conditions. A routine predischarge echo should be done to confirm valve function, ventricular function and freedom from pericardial effusion.

Homograft Root Results

PERIOPERATIVE COMPLICATIONS

In patients without active endocarditis at the time of surgery, operative mortality in the current era is 1 to 5%.^42,49,50 The risk in experienced hands is comparable to using a stented bioprosthetic or mechanical valve. Ischemic time for a root replacement with either stentless porcine or aortic homograft is approximately 90 minutes.⁵¹ A contemporary series of 100 consecutive aortic homografts (virtually all root replacements including 13 reoperations) demonstrated no hospital mortality with 100% survival at 1 year and 98% at 5 years.⁵²

In contrast, patients with active endocarditis exhibit a higher early mortality ranging from 8 to 16%.^42,53-56 PVE (17.9-18.8%) is worse than native (2.6-10%).^53,57

Hemorrhage, heart block, stroke, myocardial infarction, and wound complications occur with similar frequency to those of other AVRs, but early risk of endocarditis is lower with homografts than any other replacement valve.³⁵

Hemodynamics and Exercise Capacity

Hemodynamic characteristics of homografts are excellent at short- and medium-term follow-up, both at rest and during exercise.^58,59 A study of 31 patients demonstrated increases in peak and mean gradients of 6.6 and 3.0 mm Hg, respectively, without a significant change in effective orifice area (EOA).⁵⁸ Importantly, the EOA of even the 17 to 19 mm homografts was 1.7 cm² and larger valves approximated the normal aortic valve areas as high as 2.7 cm² for 24 to 27 mm homografts.

The typical subcoronary homograft implant demonstrates a 1 to 2 mm Hg drop in mean transvalvular gradient over the first 6 months but with full root replacement, the hemodynamic benefit is fully realized immediately. In the randomized trial of homograft versus stentless porcine root replacement the mean gradients were only 6 ± 1 mm Hg in the stentless and 5 ± 2 mm Hg in the homografts. Only one patient in each group had mild regurgitation after 5 years.⁵¹ These authors concluded that stentless and homograft root replacements are hemodynamically equivalent in the mid-term.

Long-term Outcomes

Long-term outcome has been shown to be technique dependent in a meta analysis of over 3000 patients (37% full root, 63% subcoronary) from 18 studies with a mean follow up of 12.5 years. Reoperation was significantly lower in the root replacement group.⁶⁰ There may have been some bias against reoperation in failing roots, where failing subcoronary implants were more readily subjected to reoperation.

The pioneering work of Mark O’Brien in Brisbane, Australia produced a huge series of homograft patients over nearly three decades with 99.3% follow-up.⁵⁰ This series demonstrated that rates of reoperation were lower in the full root patients (n = 3, 0.85%) than the subcoronary (n = 18, 3.3%). Of note, operative mortality was only 1.13% in 352 root patients.

Long-term durability was compromised by young age of recipient to the point that those under 20 years of age had a 47% rate of reoperation for structural valve degeneration at 10 years. Conversely, those over 60 had a 94% freedom from reoperation at 15 years and those between 21 and 60 had 81 to 85% freedom at 15 years. This series confirmed the very low incidence of thromboembolic phenomena (without anticoagulation) and a low but not insignificant rate of endocarditis.

Lund reported crude survival at 10 and 20 years to be 67 and 35%, respectively,⁴⁴ while Langley and O’Brien reported actuarial survival at 10, 20, and 25 years to be 81, 58, and 19%.^49,50

Structural valve failure of homografts increases with time, and approximates 19 to 38% at 10 years and 69 to 82% at 20 years.^44,49 Freedom from repeat AVR, for any reason, parallels structural valve failure and is 86.5 and 38.8% at 10 and 20 years, respectively.⁴⁹ As heterograft tissue technology has progressed, the difference between homograft and heterograft durability has narrowed to the point of near equivalency with both showing a dramatic age-dependent relationship with youngest patients failing most rapidly.⁶¹

Freedom from endocarditis at 10 years is 93 to 98%,^49,50 and at 20 years 89 to 95%.^44,49,50 Freedom from thromboembolism at 15 and 20 years is 92 and 83%, respectively.⁵⁰ Thrombosis of a homograft has been reported, but in the setting of lupus anticardiolipin antibody syndrome.⁶²

In patients with active endocarditis requiring AVR, results may be poorer with survival ranging from 58% at 5 years⁵³ to 91% at 10 years,⁵⁶ and is significantly lower in patients with PVE.⁵⁴ Of note, however, the risk of recurrent endocarditis is <4% up to 4 years postoperatively.^43,53,54,56 These results still compare favorably with alternatives so aortic homograft is considered by many to be the valve of choice for aortic valve or root replacement in patients with active endocarditis.

Stentless Porcine Root Results

Very few randomized trials exist comparing stentless and stented valves. Most data available are single-center case series outcomes or case cohort analyses comparing stentless valves to previously published stented valve outcomes. We present the current literature looking at perioperative outcomes, hemodynamics, and durability.

Perioperative Outcomes

Operative mortality defined as death during the index hospitalization or within 30 days ranges between 1.8 and 9.6%^61,62 with most experienced centers reporting operative mortalities around 3 to 5%. Many of the series that reported their mortality outcomes included patients who received concomitant coronary bypass or other valve surgery at the time of Freestyle root implantation making it difficult to compare these outcomes to isolated AVR or isolated bio-Bentall results. The predictors of operative mortality in these series included concomitant valve surgery, congestive heart failure, age, and coronary disease.⁶³ In a recent systematic review of the literature Sherrah and colleagues found the weighted mean for mortality to be 5.2% and 5.5% for adverse neurological events.⁶⁴

Hemodynamics and Durability

The Freestyle stentless valve is often selected for its superior hemodynamic performance that has been demonstrated in multiple series.^65,66 A meta-analysis of 919 patients by Kunadian and colleagues demonstrated that compared with stented valves, the Freestyle exhibited a larger effective orifice area index (EOAI) and lower transvalvular gradients.⁶⁷ The weighted mean difference in aortic gradients was 3.57 mm Hg which some may argue is small; however, there was a more rapid rate of left ventricular mass regression in Freestyle valve patients although this difference disappeared at 12 months. Of note the majority of valves in this meta-analysis were implanted using the subcoronary technique as opposed to the full root replacement. Although the full root replacement technique is a longer and slightly more complicated procedure, it has been shown to yield even lower transvalvular gradients.⁶⁸

The hemodynamic benefits of stentless valves are further exaggerated during exercise. In a study of 106 patients, Khoo and colleagues compared the hemodynamic performance of five different stentless and stented valves under rest and stress using dobutamine stress echocardiography.⁶⁹ They found the stentless bioprostheses exhibited a resting gradient of 9 mm Hg that increased to 16 mm Hg under peak stress. Conversely the stented porcine and bovine valves exhibited rest gradients of 15 and 20 mm Hg, respectively, that under peak stress increased to 29 and 30 mm Hg, respectively. Of note, the mean valve size implanted was 23 mm for the Freestyle, 23 mm for the stented porcine valve, and 21 mm for the stented bovine valve. There have been some early data to suggest that newer-generation stented valves have improved transvalvular gradients.⁷⁰

A number of large case series have reported excellent long-term durability of the stentless porcine prosthesis. More recently Amabile and colleagues examined a cohort of 500 patients undergoing Freestyle valve implantation.⁷¹ In this series 96% of cases were done using the modified subcoronary technique with the remaining 4% being a full root replacement. Mean age of patients was 74.5 years and 10-year actuarial survival for all-cause mortality was 44% and survival from valve-related mortality was 70%. Moreover, freedom from structural valve deterioration was 94% at 10 years yielding a cumulative incidence of structural valve deterioration of 3.7% at 10 years. When the authors examined outcomes in patients, less than 65 years at time of implantation the 10-year actuarial survival from valve-related mortality was 87%. Bach and Kon examined 15-year outcomes of the Freestyle valve in their patients with a mean age of 72 years and found a freedom from valve-related death to be 92.7%.⁷² This study found the specific causes of valve-related death to include thromboembolism, endocarditis, anticoagulation-related hemorrhage, and structural valve deterioration. The results of the Freestyle valve show it has similar durability to standard stented prostheses.